Thermal safety switch



July 21, 1942. J, M. WILSON THERMAL SAFETY SWITCH Filed D90. 26, 1940IIIIIIIIII INVENTOR v 'J @1mm M.W115oy\. BY

^ ATTORNEY Patented July 21, 1942 2,290,399

THERMAL SAFETY SWITCH John M. Wilson, Minneapolis, Minn., assignor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn., acorporation of Delaware Application December 26, 1940, Serial No.371,619

15 Claims. (Cl. 20o-116) The present invention is directed broadly to athermally actuated switch, and more particu-` larly to a switch which isbiased open but normally latched closed and which is tripped open by athermal element.

The primary object 'of the invention is to proin construction,inexpensive to manufacture, and yet durable and reliable in operation. Afurther y vide a switch of the above type which is simple at 20 and islocated between the leg I9 and the lefthand side of casing I0, as shownin Figure 1 of the drawing. The bracket;l I8 supports a pair of spacedinsulating sheets 2| between which is mounted the coils of an electricresistance heater 22. One end of this heater is connected by means ofwire 24 to a terminal 25. The other end of the heater is connectedbywire 26 to 'the terminal 21.

object is to provide a switch having a minimum l0 The threaded stem of ascrew 29 is inserted number of parts. through an oversize hole in theside of the casing Another object is to provide a thermal safety l andscrew-threadedly engages an opening in switch in which the latch ismounted on one the leg I9 of the bracket II. The leg I9 is tenblade andis latch'ed on the free end ,of a secsioned for movement toward theright as seen ond blade, the two blades compensating each in Figure 1,and, therefore, holds the head of other for changes in ambienttemperature, and the screw 29 against the outer face of the casing theswitch being carried by the latch. I0. Rotation of the screw 29 willth'erefore ad- Still another object is to provide the switch just theposition of the leg I9 and hence shift the with a manual reset memberwhich may be position of the free ends ofl the two bimetallic moved acertain distance to reset the switch, and elements I3 and I4.Theupurpose of this ada greater distance to latch itself and maintainjustment will be described-later the switch in open position. The coverfor the A third bracket 39 is connected to the base of switch maycooperate-with the reset member to the casing I0 by some suitable meanssuch`r as prevent it from being moved far enough to latch the screw 3|.A second pair of bimetallic eleitself opensc long as-the cover is inplace. ments 32 and 33 are connected at their lower These and otherobjects will readily become ends to the bracket 30 by any suitableconnectapparent as the following specification is read ing means. Theupper ends of the elements 32 in the light of 'the accompanying drawingin and 33 are pivotally connected with a metallic which plate 35 whichin turn carries an insulating Figure l is a side view of the switch withpart 30 member 36. The insulating member 39 supports of the casing beingShown in section. the stationary electrical contact 31 which coop-Figure 2 is a section taken along the line 2-2 erates with a, movablecontact 38. The movable 0f Figure 1, looking in the direction of thearcontact 39 is carried on the free end of a flexrOWS, and ible blade 39which is connected to the insulating Figure 3 iS a detail View Showingthe manual 35 member 36 as shown at 40. The lefthand end reset member inits latched position. of the member 39 extends out beyond the insu-Referring to the drawing, the reference nulating member 3B and normallyengages over the meral I0 indicates a casing for the switch mechfree endof the bimetallic element I3. A tenanism. Actually, the casing is openonly at the sion spring 42 is looped 'at its upper end over top but theside is shown as cut away in Figure 40 the members 39 and 36, and at itslower end is 1 inorder to provide a clear view of the switch loopedunder the horizontal leg of the bracket Operating mechanism. An L-shapedbracket Il II, a portion of the base of the casing I0 being is connectedto the bottom of th'e casing by any cut away to accommodate this loopedportion of suitable means, such as 'the screw as shown Iat I2. F thespring 42. The effect of this spring is to hold A pair of bimetallicelements I3 and I4 are 4" the lfthand end of the member 39 in engagementmounted at the lower ends to the bracket II and l with the free end'ofthe bimetallic member I3. are separated therefrom by means of themetallic The members 35, 36 and 39 together form in efblock I5. Theelement I4 is provided with a fect a pivoted latch member 58 and will bere- PlOjeCiOn l5 Which bears against the element ferred to as such inthe remainder of the speci- I3. These elements are adapted to warp inthe cation.

same direction on heating and two elements are The terminal 25 may beconnected by vmeans of used instead of one in order that more power -awire 44 to the upper end of leg I9 of the brackbe available foroperating the switch. et II as shown in Figure 1, or the leg I9 may be Asecond smaller bracket I8 is connected to made a separateV terminal toprovide a separate the vertical leg I9 of the bracket II as shown 55circuit through the switch. The circuit to the switch formed by thecontacts 3l and 38 may therefore be traced from the terminal 25, throughwire 44, bracket II, metallic block I5, bimetallic element I3 andilexible switch blade 39 to the movable Contact 38. A parallel circuitextends directly from the bracket II through the tension spring 42 andto the switch blade 38. The stationary contact 3l is connected by aconductor 45 directly to the bracket 30 which carries at its upper endthe terminal 4E. The switch therefore controls the circuit connectionsbetween terminals 25 and 48.

A manual reset device in the form of an inn sulating member 48 extendsthrough an opening 49 in the horizontal portion of bracket 30. The resetmember is provided with a pair of shoulders 58 which prevents its upperend from passing downwardly through the opening 9. The up,- per end ofthe reset member 48 is relatively narrow and isinserted through anopening in the members 35 and 38 and terminates slightly below theswitch blade 33 as seen in Figure i.

As stated above, the two vbimetallic elements I3 and I4 warp in the samedirection on heating and therefore provide a greater force than a singleelement fora given temperature change, although the deflection is aboutthe same. The bimetallic elements 32 and 33 also warp in the samedirection and here again two elements'are used instead of one in orderto increase the available force. Moreover, the elements 32 and 33 Warpin the same direction as the elements i3 and I4, and as the upper endsof the elements 32 and 33 carry the latch 58, it can be seen that onvariations in ambient temperature the relative position of the upper endof the bimetallic element I3 and the lethand end of the latch 58 willremain unchanged. v

When the circuit is closed through the electrical heater 22, it willbecome heated and'will gradually raise the temperature of the bracketsI8 and II on which it is mounted, as well as the metallic block I andwill, after a predetermined interval of time, raise the rtemperature ofthe bimetallic elements I3 and I4 suciently to cause the upper end ofthe element I3 to nove out from under the lefthand end of the latch 58.The time necessary for the element I3 to trip the latch 58 depen-ds uponthe distance the free end of element I3 must travel. This in turndepends upon the position of the free end of element I3 with respect tothe lefthand end of the latch 58 when the parts are cold. This relativeposition, and hence the timing of the switch, are adjustable by rotatingthe screw 29. After it is tripped, the latch will be pulled downwardlyby the spring 42 at which time the latch will pivot freely about theupper ends of the bimetallic elements 32 and 33. Movement of the latchwill be stopped by the vengagement of member 35 with the shoulders 58 onthe reset member 48, and at this .time the upper end 43 will engage theflexible contact blade 39 and cause the movable contact 38 to separatefrom the stationary contact 31, there by opening the circuit through theswitch. .At this time it will be seen that the switch is effectivelylocked in open position and can be reclosed only by a manual operation.

The resetting operation is effected by manually moving the reset member48 in an upwardly direction by pushing on the lower end 5I. This causesthe shoulders 58 to again pivot the latch 58 about the upper ends of themembers 32 and 33, and if `the members I3 and I4 have cooled, the latchmay be relatched on the upper end of the member I3. 'It will be notedthat during this operation and as long as the shoulders 58 on resetmember 48 are in engagement with the latch 58 that the upper end 43 ofthe reset mem ber is maintaining the movable contact out of engagementwith the stationary Contact. In other words, these contacts cannot beclosed by the-reset member 48 other than by relatching the latch 5B onthe bimetallic element I3 and then releasing the member 48 at which timethe ilexible blade 39 is free to cause engagement of the contacts 31an-d 38. In other words, this switch is provided with what is known as altripfree reset. l

The manual reset member 48 is provided with a latch which is shown at53. After the manual reset member is raised sufliciently far and thenmoved to the left, the bottom of the latch 53 may be made to engage withthe foot 54 of the bracket Il, thereby maintaining the reset member 48in its raised position, at which time it will be holding the contacts 3land 38 separated. This ,feature provides for a positive manual oilposition for the switch. Inorder to release the switch for movement toclosed .position again, it is necessary only to move thehandle 5I of thereset member 48 to the right, at which time the spring 42 will returnthe parts' to the position shown in Figure '1.

One of theA principal `uses of aswitch of this type is as a safetyswitch in connection with automatic oil burner control equipment. Insuch a case, the switch will be mounted on a panel along with otherdevices, such as relays vand transformer. This panel is usually providedwith a cover enclosing all of the parts, such as is indicated in partin'Figure 1 by the reference numeral 54. It is intended that the cover54 bear such a relation to the reset member-48 that with the cover inposition,.the member 48 may bey pushed upwardly far enough to relatchthe latch 58 lon the free end of the bimetallic element I3 after it hasbeen tripped, but not far enough to cause the latch 53 -to seat on thefoot of the bracket i I. The purpose of this is so that when the safetyswitch is opened for some reason, the house owner may reset the switchby pushing the member 48 upwardly without danger of latching the switchin open position. However, when the service man comes to repair the oilburner, he may remove the cover and then latch the switch in openposition to facilitate repairs. Thusthere is no danger under the normaluse of this switch of ever latching it in open position and thuspreventing operation of the oil burner, but yet a simple manual offposition is provided for the service man when he comes to make repairs.

Various changes and modifications of the above device will undoubtedlyoccur to those who are skilled in the art, and it is therefore to beunderstoodthat I am to be limited only by the scope ofv the appendedclaims and not by the specific embodiment of the invention which I havechosen to-disclose.

I claim as myinvention:

1. A thermostatic switch comprising in combination, rst and secondbimetallic blades xved at one-end and free at the other, a latchpivotally carried by'the free end of said rst blade and normallylatching on the free end of said second blade, means for causingmovement of one of said blades away from the other whereby said latchisreleased, a normally closed switch moved to open position by saidlatch upon its release, and manual reset means for said latch, said lastnamed means including means for maintaining saidswitch open until aftersaidlatch has been relatched on the free end of said second blade.

2. A thermostat-tic switch comprising in combination, first and secondbimetallic blades `fixed at one-,end and free at the other, a latchpivotally carriedby the free end of said rst blade .and normallylatching on the free end of said second blade, means for'causingmovementof one of said blades away Afrom the other whereby said latch isreleased, a normally closed switch carried by said latch, and means forcausing. opening of said switch upon release of ysaid latch, said meansacting also as a reset means for said latch and maintaining said switchopen during the resetting operation. l

ILA-thermostatic switch comprising in combination, rst and secondybimetallic blades xed at one end and free at the other, a latchpivotally carried bythe free end of said first blade and normallylatching on the free end ofl said second blade, means for causingmovement of one of ,said` blades away from the other whereby said latchis released, a stationary contact mounted on said latch, a movablecontact mounted on said latch and biased into engagement with saidstationary Contact, a manual reset member having a iirst portionengageable with said movable 'contact for separating said contacts uponrelease of said latch, and a second portion on saidreset member forvresetting said latch, said rst portion maintaining said contactsseparated during the resetting operation,

4. A thermostatic switch comprising in combination, rst and secondbimetallic blades xed at one end andfree at the other, a latch pivotallycarried by the free end of said first blade and normally latching on thefree end of said second blade, means for causing movement of one of saidblades away from the other whereby said latch isv released, a stationarycontact mounted on said latch, a movable contact mounted on said latchand biased into engagement with said stationary contact, means engagingsaid movable Contact for moving it out of engagement with saidstationary contact upon release of said latch, and means for manuallyresetting said latch.

5. A thermostatic time switch comprising ln combinaticn, a rstbimetallic blade xed at one end to a rst support and free at the otherend, a second bimetallic blade fixed at one end to a second'support andfree at the other end, said blades being so arranged that their freeends move in the same direction on temperature variations, a latchpivotally carried by said rst blade and normally latched on the free endof said second blade, an electric heater for one of said blades causingit to warp in a direction to release said latch, a nromally closedswitch moved to open position by said latch upon its release, and manualreset means including means for maintaining said switch open during theresetting operation. i

6. A thermostatic timev switch comprising in combination, a firstbimetallic blade lixed at one end to a first support and free at theother end, a second bimetallic blade fixed at one end to a secondsupport and free at the other end, said blades being so arranged thattheir free ends movein the same direction on temperature variations, alatch pivotally carried by said first blade and normally latched on thefree end of said second blade, an electric heater for one of said bladescausing it to warp in a direction to release said latch, a normallyclosed switch moved to open position by said latch upon its release, and

manual reset means including means for maintaining said switch openduring the resetting operation, and means for adjusting one of saidksupports for varying the time necessary for said one blade to releasesaid latch.

7. A thermostatic switch comprising in combination, aV bimetallic bladexed at one end and free at the other, a movably mounted latch biasedformovement in one direction, said latch including an insulating member, axed contact mounted on said member, a resilient blade xed to saidinsulating member and carrying a movable contact at a free end, saidresilient blade biasing said movable contact into engagement with saidstationary contact, said resilient blade having a portion which extendsslightly beyond 'sai'i insulating member and which is normally latchedon the free end of said bimetallic blade, means for heating said bladeto cause it to warp in a direction to release said latch, and meansacting in conjunction with said latch for separating sai-d contacts uponrelease of said latch 8. A thermostatic switch comprising incombination, a bimetallic blade xed at one end and free at the other, amovably mounted latch biased for movement in one direction, said latchincluding an insulating member, a lixed contact mounted on said member,a resilient blade xed to lsaid insulating member and carrying a movablecontact at a freeend, Vsaid resilient blade `biasing said movablecontact into engagement with said` Istationary contact, said resilientblade having "a portion which extends slightly beyond said insulatingmember and which is normally latched on the 'free-end of said bimetallicblade, means for heating said blade to cause it to warp inr adirectionto release said latch, means for conducting electric currentthrough said thermostatic switch, said last named means including saidbimetallic bladev and extending portion of said resilient blade, andmeans acting 1n conjunction with said latchl for separating saidcontacts upon release of said latch,

9. A thermostatic switch comprising in combination, a bimetallic bladexed at one end to a metallic support and free at the other, a movablymounted latch, said latch including an insulating member, a xed contactmounted on said member, a resilient blade fixed to said insulatingmember and carrying a movable contact at a free end, said resilientblade biasing said movable contact into engagement with said stationarycontact, said resilient blade having a portion which extends slightlybeyond said insulatingmember and which is normally latched on the freeend of said bimetallic blade, means for heating said blade to cause itto warp in a direction to release said latch, a spring connected betweensaid resilient blade and said metallic support for biasing said latchinto engagement with the free end of said bimetallic blade, means forconducting electric current through said thermostatic switch, said lastnamed means including said metallic support, bimetallic blade, andresilient blade forming one path, and :said metallic support, spring,and resilient blade forming a parallel path, and means actingl` inconjunction with said latch for separating said contacts upon release ofsaid latch.

10. A thermal safety switch comprising in combination, a bimetallicblade xed at one end and free at the other, a biased latch having ametallic portion normally latched on the free end o1' said blade, anelectric heater for said bimetallic blade for causing it to warp in adirection to release said latch, a normally closed switch carried bysaid latch and electrically con-- nected to said metallic portion, meansacting in conjunction with said latch for opening said switch uponrelease of said latch, and means for passing current, through saidswitch including the vlatched portions of the bimetallic blade andlatch.

1l. A thermal safety switch comprising in combination, a bimetallicblade xed at one end and free at the other, a movably mounted latchhaving a metallic portion, a spring biasing said metallic portion intoengagement with the free end of said bimetallic blade, an electricheater for said bimetallic blade for causing it to warp in a directionto release said latch, a normally closed switch carried by said latchand electrically connected to said metallic portion, means acting inconjunction with said latch for opening said switch upon release of saidlatch, and means for passing current through said switch including thelatched portions of the bimetallic blade and latch forming a rst path,said spring forming a parallel path.

12Ay In a'thermal safety device comprising a biased open switch, athermal element normally latching said switch in closed position, and anelectric heater for heating said element to cause it to warp and releasesaid switch, the combination of a manual reset member which is biased toa rst position, said member being movable to a second position in whichit operates to relatch said switch on said element following a release,said member being movable to a third position beyond said secondposition in which it maintains said switch in open position, and meansfor retaining said member'in said position.

13. In a thermal safety device comprising a biased open switch, athermal element normally latching said switch in closed position, and anelectric heater for heating said element to cause yit to warp andrelease said switch, the combina tion of amanual reset member which isbiased to a first position, said member being movable to a secondposition in which it operates to relatch saidv switch on said elementfollowing a release, said member being movable to a third positionbeyond said second position in which it maintains said switch in openposition, lmeans Afor retaining said member in said position, and

cover means preventing said manual reset member from being moved to itsthird position, but permitting movement to its second position.

14. In a thermal safety switch comprising nrst and second bimetallicbladesv xed at one end and free at the other, and a releasable bridgingmember pivotally secured upon the free end of one of said blades andreleasably latched upon the free end of the other of said blades, thecombination of, a xed contact carried by said bridging member, a movablecontact also mounted thereon, and reset means for resetting saidbridging member after it has been released by the action of saidbimetallic blades, said reset means including means for holding saidmovable contact lout of engagement with said xed contact when saidbridging member is released and during the resetting operation.

15. In a thermal safety switch comprising iirst and second bimetallicblades xed at one end and free at the other, and a releasable bridgingmember pivotally secured upon the free end of one of said blades andreleasably latched upon the free end of the other of said blades, thecombination of, switch means carried by said bridging member, and resetmeans for resetting said bridging member after it has been releasedbythe action of said bimetallic blades, said reset means including meansfor disabling said switch means when said bridging member is releasedand during the resetting operation.

JOHN M. WILSON.

